The present invention relates to a polyamide resin composition and fuel tank caps made of the same. More particularly, it relates to a novel polyamide resin composition having excellent impact strength, electroconductivity and lightweight properties. This polyamide resin composition is useful for various articles such as fuel tank caps, hoses for solvents such as gasoline, various types of connectors, door handle parts, etc.
There are known the fuel tank caps of various structures for use in many fields of industry. FIG. 1 shows a sectional illustration of an ordinary type of cap used for the fuel tanks of automobiles.
The cap 2 shown in FIG. 1 principally comprises a resin-made closure 3 which fits on a fuel filler neck 1 which opens when feeding fuel and a resin-made shell 14 covering the upper part of the closure 3.
The closure 3 comprises a cylindrical portion 4 and a top plate 8 disposed so as to close the inner periphery of the cylindrical portion at its substantially middle position in the vertical direction and having an overflow opening 9 at the center. At the outer periphery of the lower part of the cylindrical portion 4 is formed a thread 5, to engage with the filler neck 1. At the outer periphery of the upper part of the cylindrical portion 4 is formed a flange 6 adapted to detain the resin-made shell 14 in position. Beneath the flange 6 is secured a seal ring 7.
A valve body 10 constituting a negative pressure valve is disposed on the lower side of the top plate 8 in the inside of the cylindrical portion 4. The valve body 10 is held in position by a holder plate 11 which is given an upward urge by a coiled spring 12 secured to a spring seat plate 13.
The cap 2 of the above construction is set in position as its resin-made closure 3 is fitted on the filler neck 1 disposed in its mounting hole 17 formed in a fixture 16 in a fuel lid 15 of an automobile. In FIG. 1, reference numeral 18 indicates the body of an automobile, 19 a fuel feed port, and 20 the chassis of the automobile.
The conventional fuel tank caps have no electroconductivity and are therefore incapable of discharging static electricity which may be charged on the human body or clothes every time when the cap is handled. In order to solve this static charge problem, attempts have been made to impart electroconductive properties to the caps by blending an electroconductive material such as carbon black or carbon whisker into a lightweight and high-strength polyamide resin.
These attempts still have the problem that when an electroconductive material such as carbon black necessary for imparting electroconductivity of not more than 10.sup.11 .OMEGA..multidot.cm (as volume resistivity) required for the fuel tank caps is blended in a basic polyamide resin, the melt viscosity of the resin composition increases, so that it Ls difficult to conduct its operation such as injection molding. Even if the molding operation could be performed, the molded product is deteriorated in its mechanical properties such as impact strength and hardly capable of attaining an Izod impact strength (ASTM D256) of not less than 30 KJ/m.sup.2 required for the fuel tank caps.
It is known to blend a modified polyethylene copolymer in a polyamide resin to improve impact resistance.
However, there is yet available no impact-resistant electroconductive polyamide resin composition having satisfactory impact strength while maintaining electroconductivity required for the fuel tank caps by blending an electroconductive material such as carbon black and suite d for use as material of fuel tank caps.
As a result of the present inventors' earnest studies to solve the above problem, it has been found that a resin composition comprising a polyamide resin, a modified ethylene copolymer, an amide-based dispersant and an electroconductive material, shows satisfactory impact strength and electroconductivity. The present invention has been attained on the basis of the above finding.